Balloon angioplasty has been used for the treatment of narrowed and occluded blood vessels. A frequent complication associated with the procedure is restenosis, or vessel re-narrowing. Within 3–6 months of angioplasty, restenosis occurs in almost 50 percent of patients. To reduce the incidence of re-narrowing, several strategies have been developed. Implantable prosthetic devices, such as stents, have been used to reduce the rate of angioplasty related restenosis by about half. The use of such prosthetic devices has greatly improved the prognosis of these patients.
The objective in angioplasty is to enlarge the lumen of the affected coronary artery by radial hydraulic expansion. This is generally accomplished by inflating a balloon within the narrowed lumen of the affected artery. Radial expansion of the coronary artery may occur in several different dimensions, and is related to the nature of the plaque. Soft, fatty plaque deposits are flattened by the balloon, while hardened deposits are cracked and split to enlarge the lumen. The wall of the artery itself may also be stretched as the balloon is inflated. With simple angioplasty, the balloon may be threaded through the artery with a catheter and inflated at the place where the blood vessel is blocked. After the procedure, the balloon is then removed. The stent may then be used to support open the artery and may be deployed along with the balloon or after the balloon is removed. The use of a stent may reduce the risk of restenosis to 20–30 percent.
The stent may be formed from a generally tubular body that can be expanded from a collapsed configuration into a deployed configuration. The stent body may include a plurality of elongated element lengths (e.g., wire lengths, or the like) that are connected together to permit the body to be expanded. The stent may be coupled to a deployment system (e.g., a catheter) in a collapsed configuration. For example, the stent may be compressed within a lumen formed within a catheter or onto a catheter balloon. The catheter including the stent may be then advanced endovascularly (or within another vessel type) to the afflicted region of the body passage. While fed through the vessel, the stent remains in the collapsed configuration.
Once the stent has reached the afflicted region in the body passage, it may be expanded (radially) outward into the deployed configuration. The stent may be expanded into its deployed configuration by inflating the catheter balloon so that expansion of the stent is achieved in sympathy with the inflation of the balloon. Alternatively, the stent may be manufactured from a resilient material such that when it is collapsed, the stent may naturally expand from a “tense” collapsed configuration into a “relaxed” deployed configuration. In such a case, the stent self-expands as it is forced from the catheter lumen.
Given that the deployment system must typically accommodate the collapsed stent, a reduced collapsed profile size may equate to a reduced size in its coupled deployment system. As such, numerous benefits may be provided by a reduction in stent and (potentially) deployment system size. For example, as the stent is advanced to the site of deployment, it may encounter a sometimes tortuous and narrow network of vessels. Smaller sized stents and deployment systems may facilitate easier negotiation of such vessel networks. Other benefits of minimizing the deployment system may include less disruption of an atheroma and plaque that could lead to emboli, less disruption of blood flow, less likelihood of vessel wall damage, and reduced vessel puncture size for intraluminal access. Accordingly, it would be desirable to minimize the stent collapsed profile size.
U.S. Pat. No. 5,383,887 to Nadal, entitled Device for Selectively Forming a Temporary Blood Filter, describes device which can be implanted inside a vessel to form a blood filter, the device having a structure that can be expanded or compressed such that, in its expanded position, it can contact the interior of a vessel. The device includes loops for variably constricting the structure, but does not disclose loops to minimize the collapsed profile size.
PCT Publication WO 01/06952 to Fearnot, et al., entitled Stent Adapted for Tangle Free Deployment, describes an expandable stent prosthesis in which the apices of the bends located at least one end of the stent are individually twisted at an angle to the circumference of the stent to form a fan blade-like arrangement to reduce the likelihood of entanglement during deployment. The expandable stent prosthesis includes struts united at an apex with a hairpin, simple bend, or ‘safety pin’ turn in which the struts are substantially parallel in the compressed condition, but does not disclose crossing the struts to form loops.
Therefore, it is desirable to provide a stent delivery system and low profile stent that overcomes the aforementioned and other disadvantages.